1. Field of the Invention
The present invention relates to a diffusion system, and more particularly, to a diffusion system for forming an ultrathin doping layer in a wafer. The diffusion system uniformizes the concentration of a mixed gas for forming the doping layer in a short amount of time, includes a cooling rate controller for securing a high frequency response, and provides a flow system for allowing a stable gas flow.
2. Description of the Related Art
A material doped into a semiconductor device is selected in consideration of a diffusion coefficient, a solid-solubility characteristic, a mask effect of an oxide layer, and the like. Even if combined atoms are separated from a doping material during a diffusion process, the atoms must not act as another dopant atoms that may be doped into a wafer or produce an unetchable material on the wafer. A material that is doped into a wafer should have few impurities, and the concentration of the material should be easily controlled at a constant level in spite of repeated processes. Generally, a doping material remains combined with oxygen, hydrogen, or halogens such as chlorine or bromine and is categorized into a solid, a liquid, and a gas.
Meanwhile, a diffusion system includes a diffusion tube, a heater, a boat, and a dopant delivery system. Depending on the type of a wafer or device to be manufactured, the diffusion system can be categorized into a sealed-tube system, an open-tube system, a box-type system, a paint-on system, and a rapid thermal processing system.
A conventional diffusion system lacks high frequency response and robust characteristics against external disturbances, which are required to form an ultrathin doping layer with a thickness of 100 nm or less, namely, a doping layer for diffusing thermal energy. In other words, to form a nanometer doping layer, the diffusion system requires a high frequency response characteristic so that the concentration of a gas mixture can be rapidly uniformized and the speed with which a wafer that has undergone a doping process is cooled can be finely adjusted. In addition, a flow system and respective apparatuses should be closely connected to one another so as to stably supply a gas mixture and exhaust a used gas. However, the conventional diffusion system cannot systemically fulfill the foregoing requirements.